Android - List View - PopulateList

Question

My android app need to populate a ListView with a text from a web request, on a click from a button (on the toolbar). The question is, i'm working with sliding tabs with a toolbar and the list view stay on tab_1.xml . when i click on the button i have a null pointer exception on "populateList" . can anyone help?

MAIN ACTIVITY.JAVA

public class MainActivity extends ActionBarActivity {
private Toolbar mToolbar;
ViewPager pager;
ViewPagerAdapter adapter;
SlidingTabLayout tabs;
CharSequence Titles[]={"Home","Mês"};
int Numboftabs =2;
List<ValorWeb> valores = new ArrayList<ValorWeb>();
ListView valorListView;



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    mToolbar = (Toolbar) findViewById(R.id.tool_bar);
    mToolbar.setTitle("Projeto Hidro Teste");
    setSupportActionBar(mToolbar);

    valorListView = (ListView) findViewById(R.id.listView);

    adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs);

    pager = (ViewPager) findViewById(R.id.pager);
    pager.setAdapter(adapter);

    tabs = (SlidingTabLayout) findViewById(R.id.tabs);
    tabs.setDistributeEvenly(true);

    tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {

        @Override
        public int getIndicatorColor(int position) {
            return getResources().getColor(R.color.tabsScrollColor);
        }
    });

    tabs.setViewPager(pager);
}

private void populateList(){
    ArrayAdapter<ValorWeb> adapter = new ValorWebListAdapter();
    valorListView.setAdapter(adapter);
}

private void addvalor(String valor,String data){
    valores.add(new ValorWeb(valor, data));
}


private class ValorWebListAdapter extends ArrayAdapter<ValorWeb>{
    public ValorWebListAdapter(){

        super (MainActivity.this,R.layout.listview_item,valores);
    }


    @Override
    public View getView(int position,View view,ViewGroup parent) {
        if (view == null)
            view = getLayoutInflater().inflate(R.layout.listview_item, parent, false);

        ValorWeb currentValorWeb = valores.get(position);

        TextView valor = (TextView) view.findViewById(R.id.valortext);
        valor.setText(currentValorWeb.getValor());

        TextView data = (TextView) view.findViewById(R.id.datatext);
        data.setText(currentValorWeb.getData());
        return view;

    }

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}


@Override
public boolean onOptionsItemSelected(MenuItem item) {

    switch (item.getItemId()) {
        case R.id.action_refresh:

            String textFileUrl = "http://2015projetohidro.esy.es/arquivo.txt";
            String textFileText = "";

            Request httpRequest = new Request();
            httpRequest.execute(textFileUrl);
            try {
                textFileText = httpRequest.get(5000, TimeUnit.MILLISECONDS);
            } catch (InterruptedException | ExecutionException | TimeoutException e) {

                e.printStackTrace();
            }
            System.out.println("The online text file contains: " + textFileText);

            TextView textView = (TextView) findViewById(R.id.textConsumo);
            textView.setText(textFileText);

            String currentDateString = DateFormat.getDateInstance().format(new Date());

            TextView textdata = (TextView) findViewById(R.id.textData);
            textdata.setText(currentDateString);

            String currentTimeString = DateFormat.getTimeInstance().format(new Date());

            TextView textTime = (TextView) findViewById(R.id.texttime);
            textTime.setText(currentTimeString);

            addvalor(textView.getText().toString(),textdata.getText().toString());

            Toast.makeText(this,"Atualizando Consumo",Toast.LENGTH_LONG).show();

            populateList();

            return true;
        default:
            return super.onOptionsItemSelected(item);


    }
}}

ACTIVITYMAIN.XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">

<include
    android:id="@+id/tool_bar"
    layout="@layout/tool_bar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

<tabs.SlidingTabLayout
    android:id="@+id/tabs"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/ColorPrimary"
    android:elevation="2dp" />

<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_weight="1">
</android.support.v4.view.ViewPager>

TAB_1.XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"

    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="0.0000"
    android:id="@+id/textConsumo"
    android:layout_gravity="center_horizontal"
    android:layout_marginTop="45dp"
    android:layout_marginRight="81dp"
    android:textSize="45dp"
    android:textColor="@color/ColorPrimary"/>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"

    android:textAppearance="?android:attr/textAppearanceSmall"
    android:text="m³"
    android:textSize="22dp"
    android:layout_gravity="center_horizontal"
    android:layout_marginLeft="15dp"
    android:layout_marginTop="-31dp"
    android:textColor="@color/ColorPrimary"/>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="data"
    android:textSize="17dp"
    android:id="@+id/textData"
    android:textColor="@color/ColorPrimary"
    android:layout_marginTop="8dp"
    android:layout_marginLeft="45dp" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="time"
    android:id="@+id/texttime"
    android:textColor="@color/ColorPrimary"
    android:textSize="17dp"
    android:layout_marginTop="-23dp"
    android:layout_marginLeft="175dp" />

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/listView"
    android:layout_marginTop="35dp" />

TAB_1.JAVA

public class Tab1 extends Fragment {


@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view =inflater.inflate(R.layout.tab_1,container,false);



    return view;
}}

LOG

04-12 19:13:49.320  14496-14496/app.claudio.slidingtabs E/SELinux﹕ selinux_android_seapp_context_reload:  Error reading /seapp_contexts, line 16, name levelFrom, value container
04-12 19:13:59.600  14496-14496/app.claudio.slidingtabs E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at app.claudio.slidingtabs.MainActivity.populateList(MainActivity.java:70)
            at app.claudio.slidingtabs.MainActivity.onOptionsItemSelected(MainActivity.java:150)
            at android.app.Activity.onMenuItemSelected(Activity.java:2640)
            at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:350)
            at android.support.v7.app.ActionBarActivity.onMenuItemSelected(ActionBarActivity.java:152)
            at android.support.v7.app.ActionBarActivityDelegate$1.onMenuItemSelected(ActionBarActivityDelegate.java:75)
            at android.support.v7.widget.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:44)
            at android.support.v7.internal.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:76)
            at android.support.v7.widget.Toolbar$1.onMenuItemClick(Toolbar.java:164)
            at android.support.v7.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:738)
            at android.support.v7.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:802)
            at android.support.v7.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:153)
            at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:949)
            at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:939)
            at android.support.v7.widget.ActionMenuView.invokeItem(ActionMenuView.java:596)
            at android.support.v7.internal.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:145)
            at android.view.View.performClick(View.java:4476)
            at android.view.View$PerformClick.run(View.java:18795)
            at android.os.Handler.handleCallback(Handler.java:730)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:176)
            at android.app.ActivityThread.main(ActivityThread.java:5493)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1225)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1041)
            at dalvik.system.NativeStart.main(Native Method)

This is wrong man! you have list view in TAB1 xml and how can you find it in activity? find it inside fragment. This is why it is null pointer. — Harin, Apr 13 '15 at 07:27

Josef · Answer 1 · 2015-04-13T21:42:44.373

You are setting your content view in onCreate method to : setContentView(R.layout.activity_main); and in onOptionsItemSelected(MenuItem item) - you are trying to get the textViews that are not in activity_main.xml but in TAB_1.XML. So, to solve this problem you should inflate the TAB_1.XML layout and than get the all textViews.

Change your code like below :

@Override
public boolean onOptionsItemSelected(MenuItem item) {

switch (item.getItemId()) {
    case R.id.action_refresh:

        String textFileUrl = "http://2015projetohidro.esy.es/arquivo.txt";
        String textFileText = "";

        Request httpRequest = new Request();
        httpRequest.execute(textFileUrl);
        try {
            textFileText = httpRequest.get(5000, TimeUnit.MILLISECONDS);
        } catch (InterruptedException | ExecutionException | TimeoutException e) {

            e.printStackTrace();
        }
        System.out.println("The online text file contains: " + textFileText);


        //Add this line 
        View view = getLayoutInflater().inflate(R.layout.tab_1, null);

        TextView textView = (TextView) view.findViewById(R.id.textConsumo);
        textView.setText(textFileText);
            String currentDateString =       DateFormat.getDateInstance().format(new Date());
        TextView textdata = (TextView) view.findViewById(R.id.textData);
        textdata.setText(currentDateString);

        String currentTimeString = DateFormat.getTimeInstance().format(new Date());

        TextView textTime = (TextView) view.findViewById(R.id.texttime);
        textTime.setText(currentTimeString);

        addvalor(textView.getText().toString(),textdata.getText().toString());

        Toast.makeText(this,"Atualizando Consumo",Toast.LENGTH_LONG).show();

        populateList();

        return true;
    default:
        return super.onOptionsItemSelected(item);


}

Hope this will help you!!!

The log file tells : EXCEPTION: main java.lang.NullPointerException at app.claudio.slidingtabs.MainActivity.populateList(MainActivity.java:70) at app.claudio.slidingtabs.MainActivity.onOptionsItemSelected(MainActivity.java:150)

I assume that line 70 in MainActivity.java is : valorListView.setAdapter(adapter); in which you are trying to set adapter to valorListView, but because your listView (valorListView) is not in main_activity.xml this causes the NullPointerException (as @Harry mentioned in the comment) .

Delete this line in onCreate: valorListView = (ListView) findViewById(R.id.listView);

and change the populateList like this :

  private void populateList(){
        ArrayAdapter<ValorWeb> adapter = new ValorWebListAdapter();

        View view = getLayoutInflater().inflate(R.layout.tab_1, null);

        valorListView = (ListView)view.findViewById(R.id.listView);
        valorListView.setAdapter(adapter);
    }

Edit : You should to the following steps :

put all code below in onCreate instead of in populateList:

 ArrayAdapter<ValorWeb> adapter = new ValorWebListAdapter();
 View view = getLayoutInflater().inflate(R.layout.tab_1, null);

valorListView = (ListView)view.findViewById(R.id.listView);
valorListView.setAdapter(adapter);

and change populateList like this:

 private void populateList(){
    addvalor(textView.getText().toString(),textdata.getText().toString());
    adapter.notifyDataSetChanged();

 }

Remove this line :

addvalor(textView.getText().toString(),textdata.getText().toString());

from OnOptonItemsSelected(), and set all your textViews global like this :

MAIN ACTIVITY.JAVA

public class MainActivity extends ActionBarActivity {
private Toolbar mToolbar;
ViewPager pager;
ViewPagerAdapter adapter;
SlidingTabLayout tabs;
CharSequence Titles[]={"Home","Mês"};
int Numboftabs =2;
List<ValorWeb> valores = new ArrayList<ValorWeb>();
ListView valorListView;
TextView textView,textTime,textdate; //Note this line


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
   //all your code goes here...

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    switch (item.getItemId()) {
        case R.id.action_refresh:

            String textFileUrl = "http://2015projetohidro.esy.es/arquivo.txt";
            String textFileText = "";

            Request httpRequest = new Request();
            httpRequest.execute(textFileUrl);
            try {
                textFileText = httpRequest.get(5000, TimeUnit.MILLISECONDS);
            } catch (InterruptedException | ExecutionException | TimeoutException e) {

                e.printStackTrace();
            }
            System.out.println("The online text file contains: " + textFileText);

            textView = (TextView) findViewById(R.id.textConsumo);//Note this line
            textView.setText(textFileText);

            String currentDateString = DateFormat.getDateInstance().format(new Date());

            textdata = (TextView) findViewById(R.id.textData);//Note this line
            textdata.setText(currentDateString);

            String currentTimeString = DateFormat.getTimeInstance().format(new Date());

            textTime = (TextView) findViewById(R.id.texttime);//Note this line
            textTime.setText(currentTimeString);

            addvalor(textView.getText().toString(),textdata.getText().toString());

            Toast.makeText(this,"Atualizando Consumo",Toast.LENGTH_LONG).show();

            populateList();

            return true;
        default:
            return super.onOptionsItemSelected(item);


    }
}}

I understood the error and where i was missing. I did what you posted and the error disappeared, but now, my listview is not being filled — Claudio Castro, Apr 13 '15 at 15:04
when i put the addvalor(textView.getText().toString(),textdata.getText().toString()); inside the populateList he doesn't recognizes the textView and textdata — Claudio Castro, Apr 13 '15 at 17:41
I appreciate your attention, but unfortunately still not working — Claudio Castro, Apr 14 '15 at 02:59

score 0 · Answer 2 · answered Apr 20 '15 at 21:00

I passed all the code for Tab1.java that inflate the tab_1.xml and it worked!

public class Tab1 extends Fragment {

List<ValorWeb> valores = new ArrayList<ValorWeb>();
ListView valorListView;

@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.tab_1, container, false);
    setHasOptionsMenu(true);
    valorListView = (ListView) rootView.findViewById(R.id.listView);

    return rootView;
}


@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    // Inflate the menu; this adds items to the action bar if it is present.
    inflater.inflate(R.menu.menu_main, menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_refresh) {
        String textFileUrl = "http://2015projetohidro.esy.es/arquivo.txt";
        String textFileText = "";

        Request httpRequest = new Request();
        httpRequest.execute(textFileUrl);
        try {
            textFileText = httpRequest.get(5000, TimeUnit.MILLISECONDS);
        } catch (InterruptedException | ExecutionException | TimeoutException e) {

            e.printStackTrace();
        }
        System.out.println("The online text file contains: " + textFileText);


        TextView textView = (TextView) getView().findViewById(R.id.textConsumo);
        textView.setText(textFileText);

        String currentDateString = DateFormat.getDateInstance().format(new Date());

        TextView textdata = (TextView) getView().findViewById(R.id.textData);
        textdata.setText(currentDateString);

        String currentTimeString = DateFormat.getTimeInstance().format(new Date());

        TextView textTime = (TextView) getView().findViewById(R.id.texttime);
        textTime.setText(currentTimeString);

        addvalor(textView.getText().toString(), textTime.getText().toString());
        Toast.makeText(getActivity(), "Atualizando Consumo", Toast.LENGTH_SHORT).show();
        populateList();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

private void populateList() {
    ArrayAdapter<ValorWeb> adapter = new ValorWebListAdapter();
    valorListView.setAdapter(adapter);
}

private void addvalor(String valor, String data) {
    valores.add(new ValorWeb(valor, data));
}


private class ValorWebListAdapter extends ArrayAdapter<ValorWeb> {
    public ValorWebListAdapter() {

        super(Tab1.this.getActivity(), R.layout.listview_item, valores);
    }


    @Override
    public View getView(int position, View view, ViewGroup parent) {
        if (view == null)

            view = getActivity().getLayoutInflater().inflate(R.layout.listview_item, parent, false);

        ValorWeb currentValorWeb = valores.get(position);

        TextView valor = (TextView) view.findViewById(R.id.valortext);
        valor.setText(currentValorWeb.getValor());

        TextView data = (TextView) view.findViewById(R.id.datatext);
        data.setText(currentValorWeb.getData());
        return view;

    }

}}

Android - List View - PopulateList

2 Answers2